IRTF 2-30 Micron Bolometer

The IRTF 2-30 micron Bolometer ("Bolo") is a single-element gallium-doped germanium bolometer with passbands defined by a set of discrete filters. The bolometer is cooled with pumped liquid helium; the filters are cooled by liquid nitrogen at ambient atmospheric pressure. The liquid nitrogen jacket must be filled twice a day; the liquid helium is transferred twice a day. Data is recorded automatically by the IBM PC Data Aquisition System (DAS) computer, which controls filter and aperture changes remotely from the control room.

Filters, Apertures, and Windows

The filters available for use with Bolo, and associated sensitivities, are listed below:

Filter	Lambda (µm)	Delta Lambda (µm)	Limiting Mag	Limiting Flux (mJy)
1	K (2.20)	0.42	14.1	1.4
2	L (3.45)	1.05	13.2	1.5
3	M (4.80)	0.57	9.9	15
4	7.8	0.7
5	8.7	1.2
6	9.8	1.2
7	10.3	1.3	8.1	21
8	N (10.1)	5.1	9.7	5
9	11.6	1.3	7.5	30
10	12.5	1.2	7.3	32
11	Q (20.0)	9	6.5	25
12	32	5
13	Q' (20.0)	11

Notes:

• Limiting mags and fluxes are for 1 sigma detections (S/N=1) in a 6 arcsec aperture in 1 hour of integration with good sky conditions.

• The 32 µm filter has a small near-infrared leak.

The available apertures are:

• Circular with diameters (mm) of:

  Aperture Diameters (mm)
  1.0	2.0	3.0	4.0	5.0	6.0	7.0

• Two rectangular slits, 1.5 × 7.0mm, one oriented N-S and the other oriented E-W

Three windows are available: KBr, KRS-5, and CsI. The KBr window is normally used. KRS-5 and CsI windows are available for 30 µm photometry but KRS-5 has 30 % lower transmission than the KBr or CsI windows.